Locking and unlocking a mobile device using facial recognition

ABSTRACT

In an embodiment of the invention, an unlocked mobile device is configured to capture images, analyze the images to detect a user&#39;s face, and automatically lock the device in response to determining that a user&#39;s face does not appear in the images. The camera capturing and face recognition processing may be triggered by the device having detected that it has been motionless for a threshold period of time. In another embodiment, a locked mobile device is configured to capture an initial image using its camera, capture a new image in response to detecting movement of the device, determine that the device moved to a use position, capture a subsequent image in response to determining that the device moved to a use position, analyze the subsequent image to detect a user&#39;s face, and unlock the device in response to detecting the user&#39;s face. Other embodiments are also described and claimed.

This application is a continuation of co-pending U.S. application Ser.No. 14/624,443 filed on Feb. 17, 2015, which is a continuation of U.S.application Ser. No. 13/049,614 filed on Mar. 16, 2011, now issued asU.S. Pat. No. 8,994,499.

The various embodiments of the invention relate to locking and unlockinga mobile device. Other embodiments are also described.

BACKGROUND

Many mobile devices have a lock mode. The lock mode may be used toprevent inadvertent operation of a touch screen display, e.g., while thedevice is in a user's pocket or purse or when another object is placedagainst the device. The lock mode may also be used to prevent anunauthorized person from using the device. Generally, the device isprogrammed to enter the lock mode when a user presses a specific buttonor a series of buttons or when it has been idle for a certain period oftime. When a user desires to use a device that is locked, the user willtypically be required to drag a slide bar, press a specific button or aseries of buttons (e.g., to enter a password) to unlock the device.However, a user may find these steps inconvenient and time consuming.For example, a user may be reading a document using the device when thedevice detects that it has been idle for a certain period of time. Inthis case, the device will automatically enter the lock mode where itturns off or dims its display screen, and the user will be required tounlock the device before being able to resume reading the document. Inanother example, a user may be prone to forgetting the password neededto unlock the device. As a result, the user may decide to configure thedevice so that it does not automatically lock. If she then forgets orchooses not to manually lock her device, that leaves the devicesusceptible to inadvertent operation or unauthorized use.

SUMMARY

In an embodiment of the invention, a mobile device is configured toautomatically lock based on determining that a user's face is no longerpresent in images captured by the device's built-in camera. Forinstance, consider that the device is initially unlocked. In that state,a built-in camera captures one or more images, and the images are thenanalyzed to determine whether a user's face is present therein. If auser's face is not present in the images captured over a predeterminedamount of time, the device automatically locks. Thus, the device isautomatically locked when it determines that no user is currently usingthe device without having to wait for an idle timer to expire or amanual switch off by the user. The camera capturing and face recognitionprocessing may be triggered by the device having detecting that it hasbeen motionless for a threshold period of time.

In another embodiment, a mobile device is configured to automaticallyunlock. Consider that the device is initially locked. In that state, thecamera captures an initial image. When movement of the device isdetected, the camera captures a new image. The device then determineswhether it has moved to a use position (i.e., a position that indicatesthat a user is likely to want to use the device) by comparing the newimage with the initial image. If the device has moved to a use position,the camera captures a subsequent image, and the subsequent image isanalyzed to detect a user's face. If a user's face is detected in thesubsequent image, the device is automatically unlocked. This unlocks thelocked device without requiring the user to press a sequence of buttons(e.g., to enter a password) each time the user wants to use the device.

The above summary does not include an exhaustive list of all aspects ofthe present invention. It is contemplated that the invention includesall systems and methods that can be practiced from all suitablecombinations of the various aspects summarized above, as well as thosedisclosed in the Detailed Description below and particularly pointed outin the claims filed with the application. Such combinations haveparticular advantages not specifically recited in the above summary.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to thedrawings summarized below. The embodiments of the invention areillustrated by way of example and not by way of limitation in thefigures of the accompanying drawings in which like references indicatesimilar elements. It should be noted that references to “an” or “one”embodiment of the invention in this disclosure are not necessarily tothe same embodiment, and they mean at least one.

FIG. 1 illustrates an example mobile device in use.

FIG. 2 is a block diagram of some of the constituent components of anexample mobile device.

FIG. 3 is a flowchart showing the operations performed in the mobiledevice to implement the locking functionality.

FIG. 4 is a flowchart showing the operations performed in the mobiledevice to implement the unlocking functionality.

DETAILED DESCRIPTION

Several embodiments of the invention with reference to the appendeddrawings are now explained. While numerous details are set forth, it isunderstood that some embodiments of the invention may be practicedwithout these details. In other instances, well-known circuits,structures, and techniques have not been shown in detail so as not toobscure the understanding of this description.

FIG. 1 shows a mobile device 1 being held by a user 2 in a manner suchthat the device 1 is unlocked or remains unlocked by detecting a user'sface. The device 1 may be any one of several different types of smallconsumer electronic devices that can be easily held in the user's handsduring normal use. In particular, the device 1 may be anycamera-equipped mobile device, such as a cellular phone, a smart phone,a media player, or a tablet-like portable computer, all of which mayhave a built-in camera. The device 1 may have an exterior front face inwhich there is a front-facing camera 3 and a display screen 4. As willbe more fully explained below, camera 3 is used to capture an image ofthe device user 2 while the user is facing the display screen 4, inorder to unlock the device 1 or to keep the device unlocked. Camera 3may also be used to capture an image of the user 2 that may later beused to authenticate the user as an authorized user of the device 1.

FIG. 2 is an example block diagram of the device 1. The device 1includes a main processor 18 that interacts with a motion sensor 11,camera circuitry 12, storage 13, memory 19, display 22, and userinterface 23. The device 1 may also interact with communicationscircuitry 10, a speaker 20, and a microphone 21. The various componentsof the device 1 may be digitally interconnected and used or managed by asoftware stack being executed by the main processor 18. Many of thecomponents shown or described here may be implemented as one or morededicated hardware units and/or a programmed processor (software beingexecuted by a processor, e.g., the main processor 18).

The main processor 18 controls the overall operation of the device 1 byperforming some or all of the operations of one or more applicationsimplemented on the device 1, by executing instructions for it (softwarecode and data) that may be found in the storage 13. The processor may,for example, drive the display 22 and receive user inputs through theuser interface 23 (which may be integrated with the display 22 as partof a single, touch sensitive display panel, e.g., display panel 4 ofFIG. 1, on the front face of the mobile device 1). The main processor 18may also control the locking and unlocking functions of the device 1.

Storage 13 provides a relatively large amount of “permanent” datastorage, using nonvolatile solid state memory (e.g., flash storage)and/or a kinetic nonvolatile storage device (e.g., rotating magneticdisk drive). Storage 13 may include both local storage and storage spaceon a remote server. Storage 13 may store data, such as image data ofauthorized users 17 and data of movement patterns 16, and softwarecomponents that control and manage, at a higher level, the differentfunctions of the device 1. For instance, there may be a lockingapplication 14 and an unlocking application 15 that configure the cameracircuitry 12 to capture images for detection of a user's face.

In addition to storage 13, there may be memory 19, also referred to asmain memory or program memory, which provides relatively fast access tostored code and data that is being executed by the main processor 18.Memory 19 may include solid state random access memory (RAM), e.g.,static RAM or dynamic RAM. There may be one or more processors, e.g.,main processor 18, that run or execute various software programs,modules, or sets of instructions (e.g., applications) that, while storedpermanently in the storage 13, have been transferred to the memory 19for execution, to perform the various functions described above. Itshould be noted that these modules or instructions need not beimplemented as separate programs, but rather may be combined orotherwise rearranged in various combinations. In addition, theenablement of certain functions could be distributed amongst two or moremodules, and perhaps in combination with certain hardware.

The device 1 may include communications circuitry 10. Communicationscircuitry 10 may include components used for wired or wirelesscommunications, such as two-way conversations and data transfers. Forexample, communications circuitry 10 may include RF communicationscircuitry that is coupled to an antenna, so that the user of the device1 can place or receive a call through a wireless communications network.The RF communications circuitry may include a RF transceiver and acellular baseband processor to enable the call through a cellularnetwork. In another embodiment, communications circuitry 10 may includeWi-Fi communications circuitry so that the user of the device 1 mayplace or initiate a call using voice over Internet Protocol (VOIP)connection, through a wireless local area network.

The device 1 may include a motion sensor 11, also referred to as aninertial sensor, that may be used to detect movement of the device 1.The motion sensor 11 may include a position, orientation, or movement(POM) sensor, such as an accelerometer, a gyroscope, a light sensor, aninfrared (IR) sensor, a proximity sensor, a capacitive proximity sensor,an acoustic sensor, a sonic or sonar sensor, a radar sensor, an imagesensor, a video sensor, a global positioning (GPS) detector, an RPdetector, an RF or acoustic doppler detector, a compass, a magnetometer,or other like sensor. For example, the motion sensor 11 may be a lightsensor that detects movement or absence of movement of the device 1, bydetecting the intensity of ambient light or a sudden change in theintensity of ambient light. The motion sensor 11 generates a signalbased on at least one of a position, orientation, and movement of thedevice 1. The signal may include the character of the motion, such asacceleration, velocity, direction, directional change, duration,amplitude, frequency, or any other characterization of movement. Theprocessor 18 receives the sensor signal and controls one or moreoperations, e.g., the unlocking function described below, of the device1 based in part on the sensor signal.

In one embodiment, the device 1 may include movement patterns 16 thatare stored in storage 13. A movement pattern may be associated with afunction, e.g., the unlocking function, of the device 1. For example,the processor 18 may compare the sensor signal with the stored movementpatterns 16 to determine whether the user moved the device 1 to a useposition, i.e., a position that indicates that the user is likely towant to use the device. The comparing function may include employing apattern recognition algorithm or technique or a statistical model. Inanother embodiment, the processor 18 may use the sensor signal to inferor calculate tilt or inclination of the device 1 relative to a static,linear acceleration (i.e., gravity) by correlating tilt angles withdetected linear acceleration. In this way, the processor 18 maycalculate or infer when the device 1 is subjected to dynamicaccelerations by, for example, the hand of the user. In yet anotherembodiment, the motion sensor 11 may include other signal processingcircuits such as a low pass filter, a threshold detector, an amplitudedetector, or a frequency detector to remove signals representingunintended movement of the device 1. For example, a low pass filter maybe used to remove or block noise or spurious signals representing brief,unintended movement of the device or other movement of the device thatmay occur during, for example, walking, jogging, or bouncing in a movingvehicle.

In another embodiment, the motion sensor 11 may be used in combinationwith a grip detector or a proximity sensor (not shown) in the unlockingfunction of the device 1. The grip detector may be used to recognizewhen the user is holding the device 1, touching the display screen 4, orpressing a button. The grip detector may include one or more switchesand/or buttons to detect the presence of at least one finger. Theproximity sensor may sense when the device 1 is in the user's hand sothat the device 1 can ignore changes in position, orientation, ormovement that are not based on the user's hand movements and/orpositioning. By requiring the user to explicitly interact with a portionof the device 1 while moving the device 1, the possibility ofinadvertently initiating the unlocking function is minimized oreliminated.

The device 1 also includes camera circuitry 12 that implements thedigital camera functionality of the device 1. One or more solid stateimage sensors are built into the device 1, and each may be located at afocal plane of an optical system that includes a respective lens. Anoptical image of a scene within the camera's field of view is formed onthe image sensor, and the sensor responds by capturing the scene in theform of a digital image or picture consisting of pixels that may then bestored in storage 13. The camera circuitry 12 may be used to capture theimages that are analyzed by the processor 18 in the locking or unlockingfunctionality of the device 1. For example, the camera circuitry 12 maycapture an image of a facial profile of an authorized user of the device1, and this image may be stored with the images of authorized users 17in the storage 13. When the camera circuitry 12 subsequently captures animage of a user who wants to unlock the device 1, the processor 18 maycompare the facial profile in the subsequently captured image with thefacial profiles in each image of the images of authorized users 17 todetermine whether the user is an authorized user. This may beaccomplished using suitable facial recognition software that matchesfaces that look like the same person.

The operations of a lock function of a device is shown in FIG. 3, andthe operations of an unlock function is shown in FIG. 4. The operationsshown in FIG. 3 and FIG. 4 may be performed by a suitably programmedprocessor (e.g., the main processor 18 of FIG. 2) in a device. Eitherfunctionality may be activated by the user selecting a mode of operationof the device that corresponds to the functionality. For example, theuser may activate either functionality with a menu selection, bylaunching a special purpose application, or by depressing a manualswitch.

The lock and unlock functions may be used to lock part or all of adevice from use and to unlock part or all of a device for use. Forexample, the device may be turned on or off, the key pad (e.g., the keysused for dialing) may be enabled or disabled, the touch screen userinput interface of the device may be enabled or disabled, and/or dialingor sending a telephone number to initiate a call may be enabled ordisabled while still permitting the device to receive and to answer anincoming call. It will be appreciated that other functions may be turnedon or off. Furthermore, specific functions may be enabled or disableddepending on the user of the device. For example, if the unlockingfunction detects that the user wanting to unlock the device is a child,the device may enable the applications or functions that are appropriatefor a child and disable other functions such as dialing or sending atelephone number to initiate a call. The applications and functions ofthe device that are enabled and disabled by the unlocking and lockingfunctions may be configurable by a user of the device.

FIG. 3 shows the operations performed by a mobile device to implementthe locking functionality using facial recognition according to anembodiment of the invention. In an embodiment of the invention, thelocking functionality may begin, while the device is unlocked, with thedevice detecting that it is idle (block 30). The device may beconsidered idle when there is no user interaction with the device. Theuser may be considered as interacting with the device when the user, forexample, touches the display screen, presses a button, or intentionallymoves the device. The device may also be considered idle when no userinteractive foreground applications, e.g., a music player or a videoplayer, are running.

In another embodiment, the locking functionality may begin when thedevice detects that it has been motionless for a predetermined thresholdperiod of time. The device may be considered motionless when the user isnot moving the device. This may be determined using the motion sensor11, such as an accelerometer, to detect the absence of motion that isindicative of the device not being moved by the user. Alternatively oraddition to the accelerometer, a light sensor may be used to detect thatthe user is not moving the device, e.g., to detect when the device isbeing carried in the user's pocket or purse where the intensity ofambient light is normally very low. The device may be consideredmotionless even with the presence of motion that may be considered noisesuch as motion that occurs as a result of being carried by the userwhile walking or jogging, or bouncing in a moving car, or some othertype of motion that may be considered random motion or noise. The devicemay perform signal processing on the signal from the motion sensor asdescribed above to filter out the random motion or noise. For example, alow pass filter may be used to remove or block noise or spurious signalsrepresenting brief, unintended movement of the device or other movementof the device that may occur during, for example, walking, jogging, orbouncing in a moving vehicle.

In response to detecting that it has been idle according to oneembodiment or motionless according to another embodiment, the devicewill capture an image using its camera (e.g., the front-facing camera 3of FIG. 1) (block 31). The device will then analyze the image todetermine whether a user's face is present in the image (block 32). If auser's face is detected, the device repeats the operations of capturingand analyzing an image until a user's face is not detected for apredetermined period of a time or until the user interacts with or movesthe device. While the user's face is detected or the user is interactingwith or moving the device, the device remains unlocked (block 33). If auser's face is not detected in the images captured over a predeterminedamount of time (e.g., one second), the device is automatically locked(block 34). The predetermined amount of time may be a setting that isconfigurable by the user of the device. In this way, the device isprevented from automatically locking when a user is still using thedevice to, for example, read a page of an electronic book, which doesnot require the user to be pressing any buttons or touching the displayscreen.

In another embodiment, the device may continuously capture and analyzethe captured images while the device is powered on and unlocked withoutwaiting for the device to become idle or motionless. A special low powermode of operation of the camera may be used to conserve power. Forexample, the camera may be configured to capture an image at one secondintervals or the camera may be configured to capture an image in aresolution that is lower than the maximum resolution of its sensorarray. In this case, the device will automatically lock if it does notdetect a user's face for the predetermined amount of time. While theuser's face is detected, the device will remain unlocked. In thisembodiment, if a user is not looking at the display screen of the devicefor a certain period of time, the device will automatically lock withouthaving to wait for an idle time counter to expire, a motion time counterto expire, or a manual lock by the user.

FIG. 4 shows the operations performed by a mobile device to implementthe unlocking functionality of the device according to anotherembodiment of the invention. The unlocking functionality may begin withthe device capturing an initial image using its camera (e.g.,front-facing camera 3 of FIG. 1) (block 40). The device may capture thisinitial image at anytime while the device is locked. For example, thedevice may be configured to capture an initial image immediately afterthe device is locked, at predetermined time intervals, or, alternativelyor additionally, in response to detecting movement of the device. Theinitial image may be used alone or in combination with a position ororientation signal from a motion sensor to determine the reference orinitial position. This initial image and/or the initial position arestored in memory or storage of the device so that it can be used laterin the unlocking function.

After capturing the initial image, the device monitors its motion sensor(e.g., motion sensor 11 of FIG. 2) to detect movement of the device(block 41). For example, an accelerometer may be used to detect movementof the device. Alternatively or additionally, a light sensor may be usedto detect movement of the device by detecting a sudden change in ambientlight intensity (e.g., when the user takes the device out of her pocketor purse). The device may be configured to detect intended movement ofthe device. Intended movement means that the movement of the device wasintended as compared to motion that occurs as a result of being dropped,placed on a table or other surface, carried by the user while walking orjogging, or bouncing in a moving car or some other type of motion thatmay be considered random motion or noise. The device may detect intendedmovement by, for example, performing signal processing on the signalfrom the motion sensor as described above, or, alternatively oradditionally, comparing the movement pattern to stored movement patternsthat represent intended movement of the device. The device may alsodetermine that the movement is intended by sensing that the device is inthe user's hand using a proximity sensor or grip detector. Other ways ofdetermining whether movement of the device was intended by the user arepossible.

In response to detecting movement of the device, the device captures anew image using its camera (block 42). The new image may be used aloneor in combination with the detected movement to determine whether thedevice moved to a use position. The use position is a position thatindicates that a user is likely to want to use the device. The new imagemay be compared to the initial image (block 43) to determine whetherthere is a change in the position of the device, as indicated by, forexample, the change in position of the objects in the initial image andthe new image. Alternatively or additionally, the new image may becompared to the initial image to determine whether there is a change inthe ambient light intensity between the images that is indicative of theuser moving the device to a use position (e.g., when the user takes thedevice out of her pocket or purse). If the detected movement of thedevice was unintended (e.g., the device moved while still in a pocket orpurse), the new image captured by the camera will be similar to theinitial image. Comparing the new image with the initial image todetermine whether the device moved to a use position may prevent thedevice from continuing with the remaining operations of the unlockfunction, which can result in additional power savings. If the devicehas not moved to a use position, the device remains locked (block 44).If the device has moved to a use position, the device captures asubsequent image of the external environment using its camera (block45).

The subsequent image is then analyzed to detect a user's face (block46). In one embodiment, the subsequent image is analyzed for a facialprofile of a human face, without regard to a specific user. In thiscase, the device will only need to determine that a human facial profileis present in the subsequent image. If a user's face is detected, thedevice automatically unlocks (block 47). If a user's face is notdetected, the device will continue to capture and analyze images until apredetermined amount of time has elapsed. Once the predetermined amountof time has elapsed and a user's face is not detected in any of theimages, the device remains locked (block 44).

In another embodiment, detecting the user's face may also includeverifying that the user is an authorized user of the device. The usermay select that the device perform authorized user authenticationduring, for example, configuration of the device. Once the user hasselected the authorized user authentication, the user has predeterminedthat not only should there be a facial profile in the subsequent image,but that it should also match a predetermined facial profile of anauthorized user of the device. The predetermined facial profile may bedetermined from an image that was previously captured by the device'scamera and stored in a storage of images of authorized users (e.g.,images of authorized users 17 in storage 13 of the device 1 of FIG. 2).To aid the device in matching a facial profile, the display screen ofthe device may indicate where in the image the user's face must appear,while capturing the image with the predetermined facial profile andwhile capturing the subsequent image of a user that wants to use thedevice. When the device successfully matches the facial profile in thesubsequent image to a facial profile in a stored image of an authorizeduser, the device automatically unlocks (block 47). If the authorizeduser authentication operation does not successfully find a match, thedevice remains locked (block 44). Authorized user authentication is akinto a secret password or other personal security information and mayprevent unauthorized use of the device when, for example, the device ismisplaced or stolen.

It should be noted that there may be multiple authorized users of adevice. In this case, the database of images of authorized users wouldcontain an image for each authorized user of the device. To match afacial profile in the subsequent image, the device would have to comparethe subsequent image to each image in the database. Furthermore, eachauthorized user may have an associated unlocking profile in the databasethat indicates what functions or applications of the device are enabledwhen the device is unlocked.

Embodiments of the invention may include various operations as set forthabove or fewer operations or more operations or operations in an orderthat is different from the order described. The operations may beembodied in machine-executable instructions that cause a general-purposeor special-purpose processor to perform certain operations. That is, thetechniques may be carried out in a computer system or other dataprocessing system in response to its processor, such as amicroprocessor, executing sequences of instructions. Such a computerprogram may be stored or transmitted in a machine-readable medium. Amachine readable medium includes any mechanism that provides (i.e.,stores and/or transmits) information in a form accessible by a machine(e.g., a computer, network device, personal digital assistant,manufacturing tool, any device with a set of one or more processors,etc.). For example, a machine readable medium includesrecordable/non-recordable media such as, but not limited to, amachine-readable storage medium (e.g., any type of disk including floppydisks, optical disks, CD-ROMs, and magnetic-optical disks, read-onlymemories (ROMs), random access memories (RAMs), EPROMs, EEPROMs, flashmemory, magnetic or optical cards, or any type of media suitable forstoring electronic instructions), or a machine-readable transmissionmedium such as, but not limited to, any type of electrical, optical,acoustical or other form of propagated signals (e.g., carrier waves,infrared signals, digital signals, etc.).

Alternatively, these operations may be performed by specific hardwarecomponents that contain hardwired logic for performing the operations,or by any combination of programmed computer components and customhardware components. Thus, the techniques are not limited to anyspecific combination of hardware circuitry and software or to anyparticular source for the instructions executed by the data processingsystem. In addition, throughout this description, various functions andoperations are described as being performed by or caused by softwarecode to simplify description. However, those skilled in the art willrecognize that what is meant by such expressions is that the functionsresult from execution of code by a processor, such as a microprocessor.

For purposes of explanation, specific embodiments of the invention havebeen described to provide a thorough understanding of the presentinvention. These should not be construed as limiting the scope of theinvention but merely as illustrating different examples and aspects ofthe invention. It should be appreciated that the scope of the inventionincludes other embodiments not discussed in detail above. Various othermodifications, changes, and variations which will be apparent to thoseskilled in the art may be made in the arrangement, operation, anddetails of the systems and methods of the present invention disclosedherein without departing from the spirit and scope of the invention asdefined in the appended claims. For instance, the device 1 is depictedin FIG. 1 as having the camera 3 and display screen 4 disposed on thesame surface of the device; however, the camera 3 may be disposed on theopposite surface as the display screen 4 as in the case when the deviceis a digital camera. In this case, the device 1 may be configured toautomatically power up (i.e., automatically unlock) and may be preventedfrom automatically powering down (i.e., automatically lock) when itdetects a face in its frame of view. Therefore, the scope of theinvention should be determined by the claims and their legalequivalents. Such equivalents include both currently known equivalentsas well as equivalents developed in the future, i.e., any elementsdeveloped that perform the same function, regardless of structure.Furthermore, no element, component, or method step is intended to bededicated to the public regardless of whether the element, component, ormethod step is explicitly recited in the claims.

1-23. (canceled)
 24. A non-transitory machine readable medium includinginstructions which, when executed by one or more processors, cause theone or more processors to perform operations to lock a mobile devicehaving a camera, the operations comprising: while the mobile device isunlocked and in response to detecting that the mobile device has beenmotionless for a period of time, capturing one or more images using thecamera wherein detecting that the mobile device has been motionlessincludes detecting movement or orientation of the mobile device using amotion sensor; analyzing the images to determine whether a face appearsin the one or more images; and locking the mobile device in response todetermining that the face does not appear in the one or more images. 25.The medium of claim 24, wherein capturing the one or more imagescomprises capturing one or more images in response to detecting that themobile device is idle.
 26. The medium of claim 24, wherein a monitoringof a motion state of the mobile device to detect whether the mobiledevice is motionless occurs prior to capturing the one or more images.27. The medium of claim 24, wherein the motion sensor includes a tiltsensor or an infrared (IR) sensor.
 28. The medium of claim 24, whereindetecting that the mobile device has been motionless includes filteringsensor data to remove spurious signals.
 29. The medium of claim 28,wherein the spurious signals are filtered in response to a signal froman ambient light sensor.
 30. The medium of claim 24, wherein determiningthat the face does not appear in the one or more images comprises:determining that the lace does not appear in at least one of the one ormore images; capturing one or more additional images for a predeterminedperiod; and locking the mobile device in response to determining thatthe face does not appear in the one or more additional images.
 31. Themedium of claim 30, wherein the predetermined period is configurable viaa graphical interface of the mobile device.
 32. The medium of claim 24,wherein locking the mobile device comprises disabling at least a portionof a graphical interface of the mobile device and wherein a display ofthe mobile device indicates where a face must appear in an image. 33.The medium of claim 32, wherein locking the mobile device comprisesdisabling at least a portion of applications and functions of the mobiledevice.
 34. The medium of claim 33, wherein the portion of the graphicalinterface, functions or applications of the mobile device that aredisabled by the locking is configurable.
 35. A mobile device,comprising: one or more processors; a camera coupled to the one or moreprocessors; a motion sensor to detect orientation or movement of themobile device; and a non-transitory machine readable medium includinginstructions to cause the one or more processors to: capture one or moreimages using the camera while the device is unlocked and in response toa detection that the mobile device has been motionless for a period oftime, wherein the detection that the mobile device has been motionlessincludes detection of movement or orientation of the mobile device viathe motion sensor; analyze the images to determine whether a faceappears in the one or more images; and lock the mobile device inresponse to a determination that the face does not appear in the one ormore images.
 36. The mobile device as in claim 35, wherein to capturethe one or more images includes to capture one or more images inresponse to a detection that the mobile device is idle.
 37. The mobiledevice as in claim 35, wherein the motion sensor monitors a motion stateof the mobile device to detect whether the device is motionless prior tocapturing the one or more images.
 38. The mobile device as in claim 35,wherein the motion sensor includes a tilt sensor or an infrared (IR)sensor.
 39. The mobile device as in claim 35, wherein to detect that themobile device has been motionless includes to filter sensor data toremove spurious signals.
 40. The mobile device as in claim 39, whereinthe spurious signals are to be filtered in response to a signal from anambient light sensor.
 41. The mobile device as in claim 35, wherein todetermine that the face does not appear in the one or more imagesincludes to: determine that the face does not appear in at least one ofthe one or more images; capture one or more additional images for apredetermined period; and lock the mobile device in response to adetermination that the face does not appear in the one or moreadditional images.
 42. The mobile device as in claim 35, wherein thepredetermined period is configurable via a graphical interface of themobile device.
 43. The mobile device as in claim 35, wherein locking themobile device includes to disable at least a portion of a graphicalinterface of the mobile device and disable at least a portion ofapplications and functions of the mobile device and wherein a display ofthe mobile device indicates where the face must appear in an image. 44.A system to lock a mobile device having a camera, the system comprising:a non-transitory machine-readable storage device; and one or moreprocessors coupled to the non-transitory machine-readable storagedevice, the one or more processors to execute instructions stored in thestorage device to perform operations while the mobile device isunlocked, the operations including: in response to detecting that themobile device has been motionless for a period of time, capturing one ormore images using the camera, wherein detecting that the device has beenmotionless includes detecting movement or orientation of the deviceusing a motion sensor; analyzing the images to determine whether a faceappears in the one or more images; and locking the mobile device inresponse to determining that the face does not appear in the one or moreimages.
 45. The system as in claim 44, wherein capturing the one or moreimages is in response to detecting that the mobile device is idle. 46.The system as in claim 44, wherein monitoring of a motion state of themobile device to detect whether the device is motionless occurs prior tocapturing the one or more images.
 47. The system as in claim 44, whereinthe motion sensor includes a tilt sensor or an infrared (IR) sensor. 48.The system as in claim 44, wherein detecting that the mobile device hasbeen motionless includes filtering sensor data to remove spurioussignals in response to a signal from an ambient light sensor.
 49. Thesystem as in claim 44, wherein determining that the face does not appearin the one or more images comprises: determining that the face does notappear in at least one of the one or more images; capturing one or moreadditional images for a predetermined period; and locking the mobiledevice in response to determining that the face does not appear in theone or more additional images.
 50. The system as in claim 44, whereinlocking the mobile device comprises disabling at least a portion of agraphical interface of the mobile device and disabling at least aportion of applications and functions of the mobile device and wherein adisplay of the mobile device indicates where a face must appear in animage.